The prior art injectors (baseline) used here for references are the hydraulicallyactuated, electronically-controlled unit injectors described in the following references, which are incorporated herein by reference: SAE paper 930270 and U.S. Pat. Nos. 5,720,261, 5,597,118, and 5,826,562.
The first three above referenced injectors (SAE paper 930270 and U.S. Pat. Nos. 5,720,261, and 5,597,118) do not have any delay device between the control valve and the intensifier. The flow of actuation liquid into the intensifier piston chamber occurs almost immediately after the control valve opens.
The injector of U.S. Pat. No. 5,826,562 delays and limits the initial flow to the intensifier piston by adding throttle slots or a groove on top of the intensifier piston. The opening of the flow passage to the intensifier is controlled by the intensifier piston motion. In the invention of U.S. Pat. No. 5,826,562, flow to the intensifier chamber depends on the traveling velocity of the intensifier. If intensifier can not move fast enough, the flow area then cannot open up. If the flow area cannot open Lip, the intensifier cannot travel faster. This contradiction is the source of a serious limitation of an injector made according to the '562 patent.
Referring to the drawings, FIGS. 7 and 7a show a prior art fuel injector 350. The prior art fuel injector 350 is typically mounted to an engine block and injects a controlled pressurized volume of fuel into a combustion chamber (not shown). The prior art injector 350 of the present invention is typically used to inject diesel fuel into a compression ignition engine, although it is to be understood that the injector could also be used in a spark ignition engine or any other system that requires the injection of a fluid.
The fuel injector 350 has an injector housing 352 that is typically constructed from a plurality of individual parts. The housing 352 includes an outer casing 354 that contains block members 356, 358, and 360(not shown). The outer casing 354 has a fuel port 364 that is coupled to a fuel pressure chamber 366 by a fuel passage 368. A first check valve 370 is located within fuel passage 368 to prevent a reverse flow of fuel from the pressure chamber 366 to the fuel port 364. The pressure chamber 366 is coupled to a nozzle 372 through fuel passage 374. A second check valve 376 is located within the fuel passage 374 to prevent a reverse flow of fuel from the nozzle 372 to the pressure chamber 366.
The flow of fuel through the nozzle 372 is controlled by a needle valve 378 that is biased into a closed position by spring 380 located within a spring chamber 381. The needle valve 378 has a shoulder 382 above the location where the passage 374 enters the nozzle 378. When fuel flows into the passage 374 the pressure of the fuel applies a force on the shoulder 382. The shoulder force lifts the needle valve 378 away from the nozzle openings 372 and allows fuel to be discharged from the injector 350.
A passage 383 may be provided between the spring chamber 381 and the fuel passage 368 to drain any fuel that leaks into the chamber 381. The drain passage 383 prevents the build up of a hydrostatic pressure within the chamber 381 which could create a counteractive force on the needle valve 378 and degrade the performance of the injector 350.
The volume of the pressure chamber 366 is varied by an intensifier piston 384. The intensifier piston 384 extends through a bore 386 of block 360 and into a first intensifier chamber 388 located within an upper valve block 390. The piston 384 includes a shaft member 392 which has a shoulder 394 that is attached to a head member 396. The shoulder 394 is retained in position by clamp 398 that fits within a corresponding groove 400 in the head member 396. The head member 396 has a cavity which defines a second intensifier chamber 402.
The first intensifier chamber 388 is in fluid communication with a first intensifier passage 404 that extends through block 390. Likewise, the second intensifier chamber 402 is in fluid communication with a second intensifier passage 406.
The block 390 also has a supply working passage 408 that is in fluid communication with a supply working port 410. The supply port 410 is typically coupled to a system that supplies a working fluid which is used to control the movement of the intensifier piston 384. The working fluid is typically a hydraulic fluid that circulates in a closed system separate from the fuel. Alternatively the fuel could also be used as the working fluid. Both the outer body 354 and block 390 have a number of outer grooves 412 which typically retain O-rings (not shown) that seal the injector 350 against the engine block. Additionally, block 362 and outer shell 354 may be sealed to block 390 by O-ring 414.
Block 360 has a passage 416 that is in fluid communication with the fuel port 364. The passage 416 allows any fuel that leaks from the pressure chamber 366 between the block 362 and piston 384 to be drained back into the fuel port 364. The passage 416 prevents fuel from leaking into the first intensifier chamber 388.
The flow of working fluid into the intensifier chambers 388 and 402 can be controlled by a four-way solenoid control valve 418. The control valve 418 has a spool 420 that moves within a valve housing 422. The valve housing 422 has openings connected to the passages 404, 406 and 408 and a drain port 424. The spool 420 has an inner chamber 426 and a pair of spool ports that can be coupled to the drain ports 424. The spool 420 also has an outer groove 432. The ends of the spool 420 have openings 434 which provide fluid communication between the inner chamber 426 and the valve chamber 434 of the housing 422. The openings 434 maintain the hydrostatic balance of the spool 420.
The valve spool 420 is moved between the first closed position shown in FIG. 7 and a second open position shown in FIG. 7a by a first solenoid 438 and a second solenoid 440. The solenoids 438 and 440 are typically coupled to a controller which controls the operation of the injector. When the first solenoid 438 is energized, the spool 420 is pulled to the first position, wherein the first groove 432 allows the working fluid to flow from the supply working passage 408 into the first intensifier chamber 388 and the fluid flows from the second intensifier chamber 402 into the inner chamber 426 and out the drain port 424. When the second solenoid 440 is energized the spool 420 is pulled to the second position, wherein the first groove 432 provides fluid communication between the supply working passage 408 and the second intensifier chamber 402 and between the first intensifier chamber 388 and the drain port 424.
The groove 432 and passages 428 are preferably constructed so that the initial port is closed before the final port is opened. For example, when the spool 420 moves from the first position to the second position, the portion of the spool adjacent to the groove 432 initially blocks the first passage 404 before the passage 428 provides fluid communication between the first passage 404 and the drain port 424. Delaying the exposure of the ports reduces the pressure surges in the system and provides an injector which has more predictable firing points on the fuel injection curve.
The spool 420 typically engages a pair of bearing surfaces 442 in the valve housing 422. Both the spool 420 and the housing 422 are preferably constructed from a magnetic material such as a hardened 52100 or 440c steel, so that the hysteresis of the material will maintain the spool 420 in either the first or second position. The hysteresis allows the solenoids to be de-energized after the spool 420 is pulled into position. In this respect the control valve operates in a digital manner, wherein the spool 420 is moved by a defined pulse that is provided to the appropriate solenoid. Operating the valve in a digital manner reduces the heat generated by the coils and increases the reliability and life of the injector.
In operation, the first solenoid 438 is energized and pulls the spool 420 to the first position, so that the working fluid flows from the supply port 410 into the first intensifier chamber 388 and from the second intensifier chamber 402 into drain port 424. The flow of working fluid into the intensifier chamber 388 moves the piston 384 and increases the volume of chamber 366. The increase in the chamber 366 volume decreases the chamber pressure and draws fuel into the chamber 366 from the fuel port 364. Power to the first solenoid 438 is terminated when the spool 420 reaches the first position.
When the chamber 366 is filled with fuel, the second solenoid 440 is energized to pull the spool 420 into the second position. Power to the second solenoid 440 is terminated when the spool reaches the second position. The movement of the spool 420 allows working fluid to flow into the second intensifier chamber 402 from the supply port 410 and from the first intensifier chamber 388 into the drain port 424.
The head of the intensifier piston 396 has an area much larger than the end of the piston 384, so that the pressure of the working fluid generates a force that pushes the intensifier piston 384 and reduces the volume of the pressure chamber 366. The stroking cycle of the intensifier piston 384 increases the pressure of the fuel within the pressure chamber 366. The pressurized fuel is discharged from the injector through the nozzle 372. The working fluid is typically introduced to the injector at a pressure between 300-4000 psi. In the preferred embodiment, the piston has a head to end ratio of approximately 10:1, wherein the pressure of the fuel discharged by the injector is between -3000-40,000 psi.
Again the fuel is discharged from the injector nozzle 372, the first solenoid 438 is again energized to pull the spool 420 to the first position (FIG. 7) and the cycle is repeated.
In the prior art, the intensifier piston 384 starts to move immediately after control valve 418 starts to open. When a minimum pulse width command (the pulse width defining the time between the open and the close signals to the control valve 418 which permits the spool 420 to fully open (FIG. 7a) before being retracted (FIG. 7) which defines the minimum round trip time of the spool 420) is given to the control valve 418, the corresponding fuel delivery amount is referred to as the minimum fuel delivery quantity. This is illustrated in FIG. 4. If a smaller than minimum fuel quantity is desired, the controller would need to command a smaller pulse width which requires the solenoid of the control valve 418 to go through a partial motion, e.g., the spool 420 of the control valve 418 does not achieve a full open (FIG. 7a) disposition before it is recalled to its closed disposition (FIG. 7). This is less than a full round trip of the spool 420. However, partial motion of the spool 420 results in poor injector performance due to injector-to-injector variability and injection event-to-event controllability. This causes very rough engine running and undesirable emission levels.
With hydraulically-actuated, electronically-controlled unit fuel injectors (HEUI injector) as described above, the initial portion of an injection event is frequently unstable due to the aforementioned partial motion of the spool 420. Such instability is often induced by partially opening the spool 420 and then abruptly retracting the spool 420. Such partial opening is not very repeatable in a certain injector and is typically not repeatable from injector-to-injector due to manufacturing and other variances. There is a need in the industry for injectors, particularly HEUI injectors, that avoid the noted region of instability.